A chemomechanical coupling model for stress analysis of oxide scale growing between ceramic coating and substrate

The thermal growth of the oxide scale between the ceramic coating and substrate due to high-temperature oxidation is regarded as the dominating cause for the failure of the ceramic/substrate system, for example the thermal barrier coating. Based on the irreversible evolution equations, the growth strain in the oxide scale is formulated by considering the coupling effects of stress and chemical reaction during isothermal oxidation. A model which accounts for the growth strain, thermal expansion strain, and viscoplastic effect is developed for the stress analysis of the oxide scale. Numerical results reveal that there is a significant gradient in the oxide scale with the maximum compressive stress at the oxide/substrate interface and the minimum compressive stress at the ceramic/oxide interface, and the stress in the oxide scale is larger than those in the ceramic coat and bond coat. The effects of the growth strain, viscoplasticity, chemomechanical coupling, and chemical reaction on the stresses are numerically discussed.